Direct, no fluff. Below is a practical, beginner-friendly guide to diagnosing and repairing a planetary (epicyclic) gearbox on a Massey‑Ferguson MF20 baler. This covers how the system works, why it fails, every component you’ll encounter, the tools and parts you need, step‑by‑step disassembly/inspection/reassembly, testing, common mistakes and maintenance. Read the safety notes and get the MF20 service manual for exact torque and oil specs before you start.

Quick theory (analogy first)
- Think of the planetary gearbox like a tiny solar system:
- Sun gear = the sun (center).
- Planet gears = planets that orbit the sun while mounted to a carrier.
- Ring gear (annulus) = the sky dome (internal teeth) that surrounds the planets.
- Carrier = the “moon-holder” that keeps planets spaced and transfers output torque.
- Why this helps: load is shared among multiple planet gears, so the unit is compact and powerful. But uneven wear, failed bearings, or contaminated lube will quickly ruin load-sharing and cause noise, heat, and total failure.

Why this repair is needed (symptoms)
- Noises: whining, grinding, or clunking under load (especially on engagement).
- Metal in oil or oil drain plug: shiny flakes or heavy scoring.
- Excessive play or backlash in output shaft.
- Poor performance: slipping, loss of torque to baler mechanisms.
- Oil leaks or overheated gearbox.
Any of these justify pulling the gearbox and checking planetary gears and bearings.

Components — what each part is and what it does
- Input shaft / spline: brings PTO or drive torque into the planetary set.
- Sun gear: center gear on the input; drives the planet gears.
- Planet gears (usually 3–4): mesh with sun and ring; mounted on pins in the carrier.
- Planet pins / shafts: the short pins the planets rotate on; may be integral with carrier.
- Planet carrier: holds planet pins; is usually the output element (or connects to output).
- Ring gear (annulus): large internal-toothed gear around the planets; can be stationary or driven depending on design.
- Bearings: roller or ball bearings supporting shafts, carrier, and sometimes the ring.
- Thrust washers / spacers / shims: control axial clearance and preload.
- Seals and gaskets: keep lubricant in and contaminants out.
- Housing / cover: encases the gearbox; has oil fill and drain plugs.
- Fasteners, snap rings, circlips: retain gears, bearings, shafts.
- Oil/grease: gearbox lubricant (type per manual).
- Output flange/shaft: sends torque out to baler mechanisms.

Tools and supplies you’ll need
- MF20 service manual (essential for torque, oil type, shim specs).
- Basic hand tools: sockets, ratchets, wrenches, screwdrivers.
- Snap‑ring pliers.
- Torque wrench.
- Bearing puller / gear puller.
- Hydraulic or arbor press (or access to one).
- Soft mallet (brass or dead blow), punches.
- Calipers and micrometer, feeler gauges, dial indicator (for backlash/runout checks).
- Clean rags, solvent/degreaser.
- New seal kit, gasket maker, replacement bearings, planet gears (or rebuild kit).
- Shop safety gear: gloves, eye protection.
- Oil drain pan, appropriate replacement oil, threadlocker.
- Parts tray and marker to tag parts and orientations.

Preliminary safety and prep
- Park baler on level ground and secure brakes. Block wheels.
- Disconnect tractor PTO and remove drive (no accidental engagement).
- Drain gearbox oil into a pan and dispose per local regulations.
- Clean exterior to avoid introducing dirt when opened.
- Work on a bench with good light; keep fasteners organized and labeled.

Step‑by‑step repair (practical, beginner-friendly)
1. Photograph and mark orientation
- Before any disassembly, take multiple photos and mark the housing and mating flanges so you can reassemble in the same orientation.

2. Remove gearbox from baler or remove housing cover
- On MF20, many planetary units are part of the drive module — you may be able to remove the cover and work in situ, but removal gives better access. Remove any shields, chains, belts, or shafts connected to the gearbox.

3. Remove end cover / housing bolts
- Loosen in a crisscross pattern. If stuck, tap the housing gently with a dead-blow to break the seal (do not pry and bend).

4. Inspect lubrication and debris
- Look for metal flakes, scoring, discoloration. This tells you what failed (e.g., bearing failure = shiny metal; gear failure = tooth chips).

5. Extract sun gear and planet assembly
- Note how shims and spacers are arranged. Remove snap rings or retaining bolts. Use a puller or press to remove bearings and gears as required.
- Keep planets grouped with their original mounting pin/carrier location.

6. Remove ring gear if needed
- If ring is pressed or bolted, remove bolts. Check for cracks or tooth damage.

7. Inspect components carefully
- Planet gears and sun gear: look for pitting, chipped teeth, heavy wear on flanks, or polishing (sign of misalignment).
- Bearings: spin them by hand; they should be smooth. Any roughness, play, heat discoloration, or looseness = replace.
- Planet pins and carrier bores: look for ovaling, fretting or scoring.
- Thrust washers / shims: flattened, grooved surfaces indicate replacement.
- Housing bore and ring gear seat: look for damage.
- Seals: check lips for cuts, hardening, or deformation.

8. Measure tolerances (important)
- Use micrometers/dial indicator to check bearing bores, shaft runout, and ring gear roundness. Check backlash between sun and planet and planet and ring — compare to manual. If you don’t have exact numbers: any obvious looseness, binding, or nonuniform clearance = replace the worn parts.

9. Decide what to replace
- Always replace bearings and seals when gearbox is opened.
- Replace any gear with chipped teeth, heavy pitting, or hard discoloration.
- If planet carriers show oval bores or fretting, replace carrier or have it machined.
- Use a full rebuild kit if available (bearings, seals, shims, snap rings, oil).

10. Cleaning and prep
- Clean all parts with solvent, dry thoroughly. Replace fasteners if corroded. Prepare new bearings by hand-pressing or heating gears for interference fits (heat gear to ~80–120°C in oil tank/hot air — follow safe heating procedures) and pressing onto shafts.

11. Reassembly — critical details
- Fit new bearings and seals with a press; seat fully but don’t damage races.
- Reinstall sun and planets into carrier in same arrangement; if shims were present, reinstall them in the same stack order initially.
- When reinstalling ring gear/housing, ensure mating surfaces are clean. Use new gaskets or gasket maker.
- Set correct backlash/preload: this is the most critical part. Backlash and bearing preload are controlled by shims/spacers and bearing seating. Follow the manual for shim thickness. If the manual is unavailable, aim for smooth rotation with no tight spots and minimal axial play — but this is less precise; if in doubt, get professional help.
- Torque bolts to spec and use threadlocker where specified.
- Replace oil drain/fill plugs and fill to the specified level with the manufacturer-recommended gear oil.

12. Break-in and testing
- Initially run the baler at no load (engine idle, PTO disconnected if possible) and listen for any noises.
- Check for leaks.
- Reconnect and test under light load, listen and monitor temperature. After first few hours, re-check torque on bolts and re-torque if required.
- Change oil earlier than normal (after a short break-in) if lots of debris was present in the old oil.

Common failure modes and causes
- Bearing failure: due to contamination, poor lubrication, or excessive loads; manifests as rumbling or heat.
- Gear tooth pitting and breakage: caused by misalignment, poor lubrication, or shock loads.
- Carrier bore wear: high loads or fretting; creates uneven load sharing and noisy operation.
- Incorrect shim/preload on reassembly: can cause premature wear or bearing failure.
- Contamination (dirt/water): destroys bearing surfaces and gears rapidly.
- Overheating: wrong oil or low oil level.

Common beginner pitfalls (how to avoid them)
- Not photographing/marking locations — leads to assembly errors. Mark everything.
- Reusing bearings or seals — always replace these.
- Improper shimming/preload — consult manual; if unsure, have a shop set critical shims.
- Not using a press to fit bearings — hammering can damage races.
- Over‑torquing or under‑torquing bolts — use a torque wrench.
- Skipping cleaning — contamination will kill the rebuild.
- Using wrong lubricant — follow manual for viscosity and type.

Maintenance tips to prevent repeat failures
- Regularly check oil level and condition; change oil and filter per service schedule.
- Inspect seals and gaskets for leaks; keep gearbox clean.
- Avoid shock loads and make sure chains/belts that drive the gearbox are tensioned correctly.
- Replace oil after detecting metal debris; don’t keep running.
- Grease zerks (if present) and inspect bearings periodically.

Final practical advice (no-nonsense)
- If gears are visibly chipped or bearings are rough, replace the whole planet set and bearings — partial repairs often fail.
- For exact torque, shim thickness, and oil type, use the MF20 service manual — those specifics are critical.
- If measurement tools or a press are not available, consider removing the gearbox and taking it and parts to a machine shop or authorized dealer for a rebuild.
- Safety: keep hands clear of moving parts, always block the baler safely, and never work under unsupported equipment.

That’s the core: inspect, measure, replace bearings/seals/gears as needed, set correct shims/preload, clean and use correct lube, then test. Follow the MF20 manual for torque and shim specs — they’re the final authority.
rteeqp73

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Massey Ferguson 20 Bailer Knotter Servicing Part Two. Can We Make Hay With Old Farm Machines? Bailer knotters part two! further explanation of how it works. So all cleaned off and ready for re assembly. Almost!

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